A church school on the outskirts of Haiti's capital collapsed during classes yesterday, killing at least 30 children and adults and burying many more under rubble.

Around 500 people were believed to be inside the three-storey La Promesse college in Petionville when it collapsed, leaving several neighbouring houses crushed under debris.

Rescuers dug at the wreckage with shovels and bare hands, while desperate parents searched amid the broken concrete for missing children. More than 80 survivors were pulled out of the ruined building, many with serious injuries, and the death toll was expected to rise.

Michaele Gedeon, a Haitian Red Cross worker, told CNN: "The whole school collapsed on the kids. And, you know, on the phone you can hear so many, so many children, you know, crying, crying. And saying, 'This one is dead, that one is dead'."

There was no official comment on the cause of the disaster, but Petionville's mayor, Claire Rudie Parent, said that she suspected the school had a "structural defect."

UN peacekeeping troops and local police joined in the search for survivors, but the roads around the school had become so crowded with bystanders that some of the rescuers had to be brought in by helicopter. "Thirty have already been killed and there are many others under the debris," said Major Donald Hongitan of the Philippine army, who was among the UN troops. The force's Brazilian commander, Maj Gen Carlos dos Santos Cruz, said: "It's like an earthquake." Witnesses described scenes of horror at the school. One boy had his legs trapped under the rubble but begged his rescuers to cut off his feet and free him, Reuters reported.

Wailing and prayers erupted from the crowd as emergency vehicles worked their way uphill to the school and the injured were carried away. "My son who is 15 years old, he's dead. He's my only son," sobbed 40-year-old Josiane Dandin. "I don't know what I'm going to do."

Another woman screamed for her missing 12-year-old daughter. "I don't know if she is dead or alive," she said.

President Rene Preval visited the scene, and asked onlookers to come down from surrounding buildings, which engineers feared might have been made liable to also collapse.

Mayor Parent said that the school's second floor had been still under construction, while local police said that the preacher who runs the school could face criminal charges.

"There are no words for this," said the mayor.

Jimmy Germain, a French teacher at the school, told the Associated Press that the school had partially collapsed eight years ago; neighbours who lived just downhill had abandoned their land out of fear that the building would collapse on top of them, he said.

The Dominican Republic shares the island of Hispaniola with Haiti, and its health minister, Bautista Rojas, said that it was sending two helicopters to help.

Haiti is the poorest country in the western hemisphere. It is still recovering from the impact of widespread food riots this year following a string of hurricanes and tropical storms that killed nearly 800 people and destroyed two-thirds of the harvest. More than 9,000 UN peacekeepers were sent to Haiti after former president Jean-Bertrand Aristide was driven out of in a bloody rebellion in 2004.